1. Field of the Invention
The present invention relates to circuit breakers, and in particular to a draw-out circuit breaker mounted in a housing assembly and, more specifically, to a housing assembly having a bus assembly mounted therein and a cathedral door shutter assembly structured to block access to the bus assembly when the circuit breaker is removed from the housing assembly.
2. Background Information
Low voltage circuit breakers used in electric power distribution systems are commonly mounted in a housing assembly and supported on rollers which permits easy installation and removal of the sizeable circuit breakers required for such service. The housing assembly has walls forming an enclosure and a bus assembly. The bus assembly includes line and load conductors for each pole of the circuit breaker. Each line conductor, or “riser,” is, essentially, an elongated conductive bar with the longitudinal axis extending vertically through the housing assembly and the lateral axis extending toward the front of the housing assembly. The line conductors, or “runback,” are elongated conductive bars extending from the back of the housing assembly toward the front of the housing assembly and are interspersed, and offset, with the line conductors. The conductor bars are structured to be engaged by finger connectors on the back of the circuit breaker as the circuit breaker is moved into the housing assembly. In order to protect personnel from the exposed power system terminations when the circuit breaker is removed, shutter assemblies have been developed which automatically close over the conductors as the circuit breaker is withdrawn from the housing assembly, and which are opened by inward movement of the circuit breaker during installation.
The prior art shutter assembly typically included a first, stationary plate having a series of openings therein, a second, movable plate having solid portions and openings, a spring assembly and a linkage. The openings in the first, stationary plate were aligned with the bus assembly risers. The second, movable plate was slidably coupled to the first plate. In a first position, the second plate solid portions covered the first plate openings. In a second position, the second plate openings aligned with the first plate openings, thereby allowing the circuit breaker finger connectors to pass therethrough. The spring assembly biased the second plate into the first position. The linkage acted upon the second plate to overcome the bias of the spring assembly and to move the second plate into the second position. The linkage was actuated by the circuit breaker being moved into the housing assembly. The linkage and the spring assembly were typically made from metal and made from multiple parts. It is not desirable to have metal parts disposed adjacent to the circuit breaker fingers and conductors. Further, it is not desirable to have overly complex mechanisms for performing the simple operation of opening and closing the shutter assembly. Additionally, because the shutter door assembly included space for the shutter to slide laterally, the shutter assembly has a lateral width that may not fit within enclosures for smaller circuit breakers.
There is, therefore, a need for a shutter assembly that does not include sliding shutter doors.
There is a further need for a shutter assembly that does not include metal parts or has a reduced number of metal parts.
There is a further need for a shutter assembly that utilizes a reduced number of moving parts.